The present invention relates generally to the field of circuit interrupting devices. The invention relates, more particularly, to a technique for enhancing performance of a circuit interrupter by providing for deionization of arc plasma produced during a circuit interruption event.
A range of circuit interrupting devices are known and are currently in use. In general, such devices include at least one moveable contact which joins a mating contact to complete a current carrying path through the device during normal operation. In the event of an overcurrent condition, loss of a phase, ground fault, or other undesirable condition, the moveable contact separates from the mating contact to interrupt the current carrying path. Various designs of circuit interrupters include circuit breakers, single and three-phase circuit interrupters, contractors, and so forth.
Regardless of the particular configuration of a circuit interrupter, a goal is generally to interrupt current as quickly as possible, thereby limiting the total energy let through the device during the interruption event. Because the let-through energy is the integral of the electrical power through the device over time, reducing the time period required for complete current interruption is an approach to improving the performance of the devices.
As an arc expands during displacement of a moveable contact in a circuit interrupter, increased voltage investment is made in the arc, tending to reduce the time required for complete interruption. Fast-acting devices may interrupt current extremely quickly, long before a current zero crossing would normally occur in alternating current applications. In many sensitive applications, and increasingly in industrial applications, very rapid interruption with very limited let-through energy is desirable.
Although circuit interrupters have been developed which provide excellent performance, further improvement is still needed. New approaches are needed, in particular, for increasing voltage investment in arcs to drive the arc to extinction earlier than is possible through existing approaches.
The present invention provides an improved technique for interrupting current through a circuit interrupter designed to respond to these needs. The technique may be applied in a variety of devices, including devices configured to create a single arc, such as between a moveable and a stationery contact, and devices designed to create a pair of arcs upon movement of a conductive bridge or spanner. The technique promotes voltage investment in arcs created during interruption of current by deionizing arc plasma, thereby forcing replacement of ions through greater voltage investment.
In a preferred embodiment, a source element is provided in a parallel current carrying path which supports no current during normal operation. Upon initiation of interruption by displacement of a movable contact, an arc develops which expands as the movable contact is displaced. The parallel current carrying path then begins to carry current, causing surface ablation of the source element. The ablated material, such as a hydrocarbon, scavenges ions from the arc plasma, resulting in higher voltage investment. The source material transitions to a higher resistance level as a result of heating, that limits the current through the parallel current carrying path and provides protection of the source element.